Gaseous acid anhydride detection apparatus



May 16, 1950 w. F. FAGEN 2,508,238

I GASEOUS ACID ANHYDRIDE DETECTION APPARATUS Filed March 21, 1945 e Sheets-Sheet 1 5 l T6 2 224 0 x v r4 5.

May 16, 1950 w. F. FAGEN 2,508,238

' GASEOUS ACID ANHYDRIDE DETECTION APPARATUS Filed March 21, 1945 e Sheets-Sheet 2 May 16, 1950 w. F. FAGEN 2,508,238

GASEOUS ACID ANHYDRIDE DETECTION APPARATUS Filed March 21, 1945 s Sheets-Sheet 4 May 16, 1950 w. F. FAGEN GASEOUS ACID ANHYDRIDE DETECTION APPARATUS 6 Sheets-Sheet 5 Filed March 21, 1945 Ill May 16, 1950 w. F. FAGEN GASEOUS ACID ANHYDRIDE DETECTION APPARATUS Filed March 21, 1945 6 Sheets-Sheet 6 Patented May 16, 1950 2508,238 ("meshes Aoio' Armyniti'fiif APPARATUS William F. Falgeh; Indianapolis, Ind.-,= assigx'ioi' to stewart w'arner Corporation; Chicago; 111;, a"

corporation inf-Virginia semantic-H 21, 194?; seeimarss'szsw 14 Claims:

Theihvntion re1at esgeheia11y ti) al-n-im'provii methoda'nd apparatus for the detection of gas eons acid 'anhyd-ride's and percur'ser's thereof, such ieeexamme, as carbon-marinade,- ca-rbori dioxide; sulphur dioxide, and the like;

It is frequently of greati-inportande to'beable to detect the" presence of very sinail concentratio'nsmf carhoii'monoxidet- For example, men craft there have been some instances of mendhas of"thecrewbeirig'injuriousiy afiected-by carm'onoXidefroni-the exhaust of the engines, andir'oihotheneduipnientw A 'sis-wei1 known; carbon monoxide is odorless and' its e'ii'ecttsjare' therefore particulafrlyvicious because-the person aiieted does not have" an oppoitiinit'y totake; anyrecautions or counter -nieasures-w Likewise; heating systems of buildings occasionally are damageem aieoperated improperly; and rh'akef it po'ssibieforsome of-thefiu gases to niix withthefair being heated; a p

In nia11yinsta-I'ices itis therefore of extremely great advantageto have" availablea method and apparatus for thedetection-of carbon monoiiidef ahiifg'eseousacidanhydrides; and to provide'a i indication or'f warning signal whenever the concentration of such noxious gases 'apprda'ches percentages. To be useful in accom'plish'ing'g th'is purpose; the apparatus must-be rugg'edi should operate either ntmuous wcyneany at short: innervate, shouldb'e light iiiweightiportahie; and seif regenratiiief v I h p The presence of'acid anhydritlesin airmayhe" deterx'r'iinei by passing the air "through an a a oiis" solution anoirrieasurin thepI-i value of thesolution;

Inthecon'ventiona1 method for the determinatioii f'va1ue,' or hydrogen ion 'concentration'; a glass electrodefis u'sd and the 'potentiahdiff ference *electronica11y '-amp1ifiedto provide 9; Volt age suitable for indication. Due principally to the extreme fragilityof the glass electrode, such" apparatus is not suitable-for general commercial use, particularly onaircraft andthe'like where theiapparatus may be subjected to severe shock and vibration? Furthermore; the voltages gen ratd by such g1asse1ectrode apparatus are in" the -xiiicrovoltfr'a'n'ge' so that they "cannot be" used practically for indication or" control purposes without amplification; In the apparatus of the present invention, it is not necessary to employ a glass electrode; or to utilize an electronic amplifier; sir'iee the voltages generated by the cietec} ti cell are in the order' of several millivo i tsfi which is sufiicientl y high for the direct o era: ti'on sensitiife' electromagneticrelay:

'th s th'e "primary objectof the intention to" prev-me a'n' iniproved' 'apparat'us andmethod for the detection ofminute concentrations in' the i ames-thereonc-areonmeiiox 'e acid anhydri'd s;- aria: gases =capab1e -of forrhi iig acidanhyirid s1 66' A further dbjct is to provide" an improved apparatus of high sensitivitfiwhich may be used to indieate 0'1 toprovide an alarm when the atmosphere contains caebdnmonoxide 01" any simmeras;

i ither object is to provide" an improved systemamapsaratus -rdr generating asubstantiai electric current steamers" exists an ap premame aifiereaee'm hydrogen ion concentration i-ii tvvopa'rti-aiiy segregated portions of aqueous medium. v i A H A further object is to provide-'- an improveda'ppa atus of the above mentioned type, in which 'i i by ed for cofhpensating for variations in atmosphric pressu e further object is to provide an i pr ved for" raisins the atmosphere the apparatus. lei-' sweet is as; prov de im rove means for preventing loss of'the aqueous S0111" tion teenage 'a-ispersiona'fiavaporization in the ferceii through the apparatus. A further object is t0"provide"an ihiprovii" a" s'ior th'e det' tion-of thepresenceof use inthe'atmosphere, in which means are provided fo'r'readiiy cheek ing the oper-ativecondition of theapparatus.

A further object is to provide an improved control and indicating circuit arrangement for ,gzaseou's anhydride' detection apparatus.

AF'furth'er'ob jct-is 'tdp-roVide an improved means for ins'uring accuracy of the indications in: a-gaseohsnrihyd'zid detection apparatus', by maintaining the" sensitive" elements" thereof at cb'nstaht temperature;-

A' further: object of th "invention is'to rovide air improved apparatuspf theaoovementioned" typejinwvhich the voltage generated in the de"-" teetion ce'li'is 'sl'iiiicintl'y high for the direct" operationo'f an electromagnetic" relay;

A' further'pbje'ct is to provide an improved ap paratus owne -abovementiond'type; which dues not requirethe use car-mnemonic am lifier;

A fu'r'iiherobjectis to provide an improved" apparatus ofthe ahoveme'nti'oned type," having visual iiieans fofiiidicatinig the flower the gases through it? A further ohjet -is"-to provide an improved ai 'p'aratus for the -o1ete'ction of presence of "sem A. women 'anhydr'i'des' iii the tmosphere; which Fig. 3 is a circuit diagram of the electrical portions of the apparatus;

Fig. 4 is a fragmentary sectional view of a filter forming part of the apparatus;

Fig. 5 is a fragmentary sectional view of the high speed pump used for forcing atmospheric air through the apparatus;

Fig. 6 is a sectional view of an improved absolute pressure responsive relief valve;

Fig. '7 is a sectional view of a loaded check valve forming part of the apparatus;

Fig. 8 is a longitudinal sectional view of means utilized to saturate the air circulated through the apparatus with water vapor;

Fig. 9 is a longitudinal sectional view of the soda lime filter for removing carbon dioxide and similar gases from the air;

Fig. 1G is a longitudinal sectional view of an improved two-way valve;

Fig. 11 is a longitudinal sectional view of an improved burner forming the means for causing the carbon monoxide to combine with oxygen in the air to form carbon dioxide;

Figs. 12 and 13 are transverse sectional views taken on the lines |2l2 and i3l3, respectively, of Fig. 11;

Fig. 14 is a front elevational view of the flow meters;

Fig. 15 is a side elevational view, with the parts thereof in fragmentary section, taken on the line l5i5 of Fig 14;

Fig. 16 is a vertical sectional view of the detection cell;

Fig. 17 is a fragmentary sectional view taken on the line I'l-H of Fig. 16;

Fig. 18 is a plan view of the filter material retaining discs which are shown at lines l8l8 and ISa-lBa of Fig. 16; and

Fig. 19 is a vertical sectional view of the rectifier used to remove excess moisture from the gas as it leaves the detection cell.

General description In order that the following detailed description of the invention may be more readily comprehended, it is preceded by this brief general description of the method and apparatus.

Referring particularly to the flow diagram of Fig. 2, atmospheric air is drawn into the apparatus through a pipe 28 through a dust filter 22 by means of a pump 24, the pump discharging past a pressure relief valve 26 and past a suitable check valve 28. The air passing the check valve 28 fiows to a saturator 30 which contains distilled water and is provided to assure that the discharge therefrom will be of uniform humidity irrespective of the humidity of the atmosphere. The humidified air flows from the saturator at through a soda lime filter 32, which functions to remove CO2, S02, and similar gases, but which does not remove CO. In normal use of the apparatus, one-half of the gases thus scrubbed by the soda lime filter flow through a suitable flow meter 34, past an adjustable restriction 35, into one compartment of a detecting cell 38. After passing through the cell 38, the gases pass through a rectifier 40 by which excess moisture is removed and returned to the cell 38, the discharge from the rectifier being under the control of an aneroid bellows regulated absolute pressure relief valve 42.

The other half of the air discharged from the saturator 30 flows freely through a two-way valve 44 to a burner 46, which in its preferred form comprises a platinum wire heated to incandescence so that any CO flowing with the air is oxidized or burned to form C02. The mixture of CO2 and air from the burner 46 flows through a flow meter 48 past an adjustable restriction 50 to the other compartment of the cell 38, thereafter flowing with the other part of the air stream through the rectifier ll] to the pressure relief valve 42 from which it is discharged to the atmosphere. Due to the provision of the pressure relief valves 26 and 42, the pressure of the air and gases in the flow circuits between these two valves is maintained at a constant value irrespective Of the changes in atmospheric pressure.

The cell 38 may be described generally as containing two interconnected compartments containing an aqueous solution of potassium chloride, one for the flow of that part of the air stream in which the CO has been burned to form CO2, and the other part in which CO, in the concentration of the atmosphere, is present. Within each of the compartments of the cell 38 is an electrode, preferably of sheet platinum. When CO, that first has been burned to CO2, flows through one of these compartments, and dissolves in the potassium chloride solution present therein, the electrical state or electrical activity of the resulting liquid will be different from that of the solution in the other compartment, through which unburned CO flows. An essential reason for this difference in electrical activity is that the CO2 increases the hydrogen ion concentration of the solution in which it dissolves; whereas the hydrogen ion concentration of the other solution, in which the CO dissolves only to a slight extent, undergoes substantially no change. This difference in electrical activity between the two solutions is reflected in a difference of potential between the electrodes in the two compartments. This potential difference accumulates; that is, for a limited time the voltage between the cells builds up.

The apparatus is operated in a regenerative cycle. For an interval of approximately 30 seconds, the burner is energized and thus a potential is built up on the electrodes of the detection cell. During this 30 second interval, the sensitive relay is disconnected from the cell electrodes. During a following interval, such as 30 seconds, the burner is deenergized while the sensitive relay is connected to the cell electrodes. Thus the potential stored up on the electrodes of the cell operates the relay, provided there has been a sufficient concentration of CO in the atmosphere being analyzed. Also during the second interval the cell is balanced or normalized because the gases flowing through both compartments of the cell are of identical composition.

Operation of the sensitive relay may be utilized to complete a circuit through a more rugged relay and the latter may be utilized for the energization of any desired signal indicator, or may be used for the control of other apparatus.

Panel and chassis Referring to Fig. l, the apparatus is illustrated as being mounted in a casing 5| preferably made of thin light weight sheet metal such as an aluminum alloy, having a door 52 hinged thereto. The apparatus comprises a front panel 54 apertured to receive the Window of the flow meters 34 and 48. A valve control knob 56 projects from the front of the panel while a sensitive relay 58 has some of its operating parts visible through an opening formed in the panel. A pair of water a-cosgase lever gauges 6 and 62 and an indicator lamp 6!" are likewise visible through suitable openings formed in the panel 54. An eiectrical connec tion socket 36 is secured to the panel for making connection with a source of power and with other apparatus to be controlled. The apparatus is mounted on a suitable chassis of which the panel 54 forms a part, this chassis may be enclosed or partially enclosed by an internal housing 68, and the space between the housings i] and 68 is filled with a suitable heatinsulating liner I0 which may bear cork or other suitable material.

Air filter Referring to Fig. l, the glass wool filter 22 re ceivesair from the atmosphere to be analyzed through the pipe 253 suitably connected to a fitting. 1 2" which is welded or otherwise suitably secured to 92 pressed sheet metal casing half 74, the other half of the casing being secured to the half I4 by welding or other suitable means. The Gas-- ing 14, 1 5 is filled with compressedglass wool Iii for removing grit and dust from the air.

High speed air pump The-cleaned air is drawn from the filter through atube 78 which is connected to the inlet fitting of a high speed pump or compressor 82. This pump comprises a body having a bracket 85 secured thereto. A high speed motor 88 is suitably secured to the bracket 85, this motor operating at a speed in the order of 6,000 PL. P. M. The armature shaft of the motor 88 has a counterweight secured to the end thereof, this counterweight having a crank pin 92 projecting therefrom. A connecting rod 9 has a ball bearing assembly 96 forming a rotary bearing connection with the crank pin 92 and has a similar ball bearing assembly 98 providing a pivot connection to a wrist pin I 00 carried by a piston rod sleeve I62. A piston rod IN is suitably secured in the sleeve I02. 7 A piston I66, which is preferably made of carbon, surrounds the piston rod its and is secured between a flange I68 formed on the latter and the lower end of the piston rod sleeve I02. The piston IDS is reciprocable in a cylinder liner Ilii' which is preferably made of stainless steel and is provided with an inlet port I I2 in registry with an inlet port I I' l formed in the body 85%. The piston rod sleeve It?! is guided in a suitable bearing H6 which is secured in the bracket 86. ports II8 are formed in the bearing H55 and bracket 8-6 to permit free communication between the atmosphere and a space I261 at the upper end of the cylinder.

An outlet port I22 is located in axial alignment with the cylinder lit and is of sufiiciently large diameter freely to receive the projecting end of the piston rod ltd. A valve seat In is formed around the lower end of the outlet port I22 for engagement by a reed-typecheck valve I26 which is clamped to the body 3 by a plate I28. The plate I2 8 is suitably iorrned to receive a discharge or outlet fitting I38, suitable gaskets I32 being providedon either side of the check valve I 26.

It will be noted that this pump operates at extremely high speed and therefore may be made very small and light in weight while pumping an appreciable quantity of air.

'' Absolute pressure relief valve and check valve The outlet fitting 313 of the pump is connected by a tube I34 (Fig. 6) and a T I36 to the pressure relief valve 2%. This valve comprises an airtight housing It B within which there is located an evacuated bellows Mt having :one end thereof Registering clamped to the housing I38; and its other end can: formed to receive a valve disc I42 which maybe made of rubber or a suitable rubber substitute. This valve disc normally engages a valve seat I formed at the inner end of an: outlet nipple I 46 which is threaded in a bushing. I48 and after be ing adjusted is preferably made airtightby a suitable sealing compound I50.

From the foregoing description of the absolute pressure relief valve 26, it will be apparent that this valve will operate to permit escape to the atmosphere of some of the air pumped by thepump 82 when the absolute pressure exceeds a value for which the valve is set. Thus air under con-' stant absolute pressure is supplied through pipe I52, also connected to the T I36, to the check valve 28 (Fig. 7). The primary purpose of this check valve is to prevent return flow to the pump 82 when the latter is stopped. This check valve may be of any suitable construction, but is illustrated as comprising a housing I54 closed by a cap I56 upon which is formed an annular valve seat I58. The check valve comprises an annular disc IEO of rubber or similar material retained in a valve member i622, the valve member having a fluted stem ltd forming a loose guide. The valve is held against its seat by alight compression coil spring Hit. A tube 46-8 is connected to the lower end of the check valve body I54 Water vapor saturator E'he tube $8 is connected to aninlet fitting I'iil (Fig. 8) of the saturator 3c, the fitting II'El' having a frusto-conical surface l2 form-ing a tight seal with the lower end of a tubular body l 14, preferably made of Sarah, a vinylidene chloride thermoplastic. The inlet fitting H0 also clamps a porous rubber disperser lie against a slotted washer I18, the latter abutting against a suitable shoulder formed within the body I'M.

a ative to remove droplets of water which might otherwise be carried from the saturator. The upper end of the tubular body IN is closed by a plug I while a T I92 has one leg threaded into the body I'M in communication with the space directly beneath the plug I90. A water level gauge tube 62 has its ends secured to the body I74 in hermetically sealed relationship. By making the body "4 and the gauge tube I94 of Saran, the ends of the gauge tube I98 may be joined to the body I'M by applying heat and pressure. The saturator is partially filled with distilled water which may be replenished from time to time by unscrewing the plug I96. The purpose of the saturator is to secure substantially 100% humidification of the air forced through it, so that the initial humidity of the air being analyzed will not have any effect, and further, to prevent excessive loss of water from the detecting cell, which would occur if the air dispersed through it were not thoroughly humidified.

Soda lime filter A tube I96 connects one branch of the T I92:

to the soda lime filter 32 (Fig. 8), while the other branch of the T I92 isconnected to the two-way ram 44 by tubing I98. The soda lime filter is shown in Fig. 9 as comprising a tube 260 of Saran or similar material, which is suitably bonded to end caps 202 and 233. Within the tube 2%. adjacent both the bottom and top thereof, are wads 2M, 205 of glass wool or similar material which is utilized to retain granules 268 of soda lime (CaO-i-NaOH) Flow meters and adjustable flow restrictions The outlet at the upper end of the cap 263 is connected by a tube 2&8 with a T 245 (Fig. 2), one branch of this T being connected by a tube 2l2 with the two-way valve it, while the other branch thereof is connected by a tube 2M with the flow meter 3t. As shown in Figs. 14 and 15, the flow meters 3% and 28 form part of a unit comprising a body 2M5 to which the tube 2M and a tube 258 are connected by elbows 22G. Suitably secured in the body .255 are the similar transparent indicator tubes 34 and 48 which may be glass but which are preferably made of Saran and thus may readily be sealed to the body 2H5 by application of heat and pressure. The flow of air upwardly through the tube at results in forcing an indicator element (not shown) upwardly, and since the bore through the tube tapers out wardly in an upward direction, the clearance be tween the indicator element and the walls of the bore increases as the indicator element is raised. The heights of the indicator elements thus show the flow rates, which may be read on the adjacent suitably calibrated graduations. Such flow meters are of well known construction and therefore have not been illustrated in great detail.

At the inlet of each of the fiow meters, there is a seat 222 for a needle valve 22d which may be adjusted by means of a knurled knob 22. These knobs project in front of the panel Q (Fig. 1) and are adjusted to provide the restrictions indicated diagrammatically in Fig. 2, as the restrictions 36 and 5i], to cause the flow rates through the two meters to be substantially equal.

Two-way valve The two-way valve shown in Fig. 10, which is not necessarily a part of the apparatus, comprises a valve body 233 having internal valve seats 232 and 233 for engagement by annular valve discs 234 and 235 suitably secured to a valve plunger 23%. The valve plunger 236 is sealed to the body 239 by a flexible elastic diaphragm 238 made of rubber or the like, and has its outer edge bonded to a ring 2% and its central portion bonded to a sleeve 242, the latter pressed over the plunger 236. The plunger is urged to the right by a compression coil spring 24 normally to maintain the valve 235 closed against its seat 233. The plunger 232i is provided with the control knob 56, the plunger being guided :in a bushing 246 by which the valve is secured to the panel 5 1, and by which the ring 246 is clamped between sealing gaskets.

A tube I98 connects the T 592 (Fig. 8) with the valve body 230 so as to have its flow controlled by the valve 235. It will be noted from Fig. 10 that the two-way valve is normall in such position that air may flow freely from the tube 2:2 through the valve body, and flow therefrom through a tube 2 38.

The burner The tube 248 has its other end connected to the burner 46, which comprises a metal tube 258 (Figs. 11-13) having apertured end plugs 252 and 253. The plugs 252 and. 253 are conformed to engage bead-like seals 254 and 255, respec tively, formed on the tubes 258 and H8. The tube 248 is thus insulated from the plug 252 and is utilized as a conductor for supplying current to a coil 256 of platinum wire wound on a suitable form 258 of soapstone or similar insulating and heat resisting material.

As best shown in Figs. 12 and 13, this form 258 is of generally triangular shape in transverse section and has three arms 26% at each end for 10- cating the form centrally within the tube 250. One end of the coil of platinum wire 256 is brazed to the end of the tube 248, while the other end is suitably brazed to the tube 255. Thus electrical connections may be made with the tubes 248 and 250 to supply energizing current to the wire 2%. There is substantially three point contact between each turn of the coil 25b and the form, so that the major portion of the surface of the wire is exposed to the air flowing through the burner.

When the burner is energized, the wire 256 is raised to the temperature of incandescence and thus any CO in the air will 'be combined with the oxygen to form C02.

The part of the air which has thus hadits CO content converted to 002, after passing through the flow meter 48, flows to one compartment of the detection cell 38 through a tube 262. In a similar manner the other part of the gas sample, after flowing through the flow meter 34, passes through a tube 26d leading to the other compartment of the detection cell.

Detection cell As shown in Fig. 16, the detection cell comprises a tubular body 266 preferably made of Saran. A pair of chimneys 263, 259, likewise made of a suitable insulating material such as e Saran, have their lower ends flared and secured to the body by inlet bushings Ziii and 2H, respectively, to which the tubes 262 and 26-; are connected. The upper ends of the chimneys 238, 269 fit in suitable recesses formed in a locating plug Zli which has a central drain opening 214 and the upper surface of which is dished to conduct water to the drain opening. Also secured to the locating plug 212 are a pair of perforated caps 216, 271, which aid in separating any water mist or droplets which may be carried with the air. At the lower end of each of the chimneys 268, 2S9, there is a compressed glass W001 microdisperser 286?, each of which is retained between a pair of slotted washers 282 (Fig. 18) the upper washer of each pair being pressed against a shoulder formed within the chimney, while the lower washer of each pair is held in position by a tube 28 1, the upper end of which is slotted to permit free flow of the air.

It has been found that substantially any desired degree of microdispersion of air in the liquid may be obtained by varying fineness or the degree of compression of the glass wool. This microdisperser has a reasonable amount of resistance to damage by freezing and shock, and has been found to be stable with respect to continued deep vertical corrugations so as to provide large surface areas in contact with the liquid within The interior of each of the chimneys. 268, 269 is in free communication with the interior;-

the cell.

oi thebody 266 through a plurality of perforations 2 -8-8 located directly beneath. the electrodes 286, 281-.

Y The cell is partly filled with an aqueous solution, preferably a 1- N solution. of KCl, that is, a solution of about 75' g. of. KCl per liter of distilled water. The extent to which the body is filled with the solution may be observed through the panel by the height of the liquid in the tube 68, the latter being preferably made of Saran and having its ends homogeneously joined. to the body 266 by the application of heat and pressure.

Conductors 293 and 29! are respectively connected to platinum foil. electrodes 2%- and. 23?, as by welding, and lead from the body 263 through sealing fittings 294. Each of these fittings comprises a nipple 29 6 sealed tothe body 235- and having a. cap 23-3 threaded thereto. The conductors 293- and 2.31 each. has a glass bead 233 fused thereon and this glass bead isclamped between the fitting 236 and cap 233 so as to form an airtight insulating'seal' for the conductor 230.

"The. top of the tubular body 236 is closed by a plug 333 which has. a frusto-conical surface 3% for making an airtight seal. An elbow 334 is "threaded into the body 266 above the locating plug 2 12 and forms an outlet which is connected by a tube 336 to the rectifier 43.

To insure uniformity of operation of the cell 3.8, it is preferably maintained at a constant temperature. It has been found that the sensitivity is greatest through the range from 110 F. to 140 F. To maintain the temperature of the so lution in the cell at a value within this range, e. g., 120 F., there is provided a thermostatically controlled heater comprising a rectangular high resistance wire 3&8 coiled about the lower portion of the body 26.6 and insulated therefrom by a mica sheet 3E3. A similiar mica sheet 3l2 surrounds the coil 308 to insulate it from a surrounding shield 3M.

Suitably secured to the shield 354 is a thermostatic switch. comprising a bimetal 3l5 having one end rigidly secured to the body 266 and having its initial flexure adjustable by means of an adjusting screw 3l8. The bimetal 3l6 operates a switch arm 32 which is adapted to make contact with a. switch arm 322 and thus complete the circuit to. the heating element resistance wire 338. The thermostatically operated switch may be of any conventional snap acting construction.

Rectifier As shown in Fig. 19, the rectifier 4!! comprises a tubular body 3224. Within the cylindrical bore of the body 324 there is a plug 326 which has a helical fin 328 having a press fi-t with the bore, thereby to form. a helical passageway for the flow of. air. Due in part to the centrifugal action, air flowing through this helical passageway has any droplets carried therewith thrown against the wall. of. the bore so that the air leaving the upper end. of this passageway is substantially free from condensed moisture. Any water separated from the air flows downwardly along the helical. passageway. and may drain back into the upper end of. the detection cell through the tube 306.

The heat generated by the heating coil 308 of t the rectifier 40 and the condensation of moisture within the latter will therefore be increased. Thus net evaporation of the water in the cell will be at an insignificant rate.

Electrical components and circuits therefor Referring to Fig. 3, the various electrical components of the apparatus are shown diagrammatically together with the circuits connecting them. In this diagram the apparatus is assumedto have been designed for operation on an airplane customarily having a 24 v. direct current. power supply.

The apparatus may be energized by closing. a manually operated main switch 33!], thereby en, ergizing. lineconductors LI and L2. Assuming that the cell 38 is at a temperature below F'.,. the thermostatically operated switch 328 will be closed and the heating element 3m. immediately energized. Likewise, the pump motor 88 will; be immediately energized to start pumping air through. the apparatus- A. constant speed motor 332 is likewise immediately energized, this motor driving a. suitable speed reducing gear train for lthe operation of. a pair of switches 334 andv 335,

The driving connection between the motor gear train and the switches 334 and 335 is such that when the switch 334 is opened the switch 335 is. closed, and vice versa. The timing ispreferably such that a complete cycle of opening and closing of these switchesv takes place in one minute.

each switch being. open for one-half minute and.

closed for one-half minute.

The switch. 334, when closed, supplies current r. to the platinum burner 253, while the switch 335.

when closed connects the cell. output lead 291 to the sensitive relay 58, the other lead 293 of. the. cell being permanently connected to the other terminal of the sensitive relay 58, which. may be. of the. Weston Sensitrol type. Connected in parallel with the switch 335 is a resistance 336,. adjustable to a relatively high value, for example, adjustable from zero to 5 megohms, and. used in the calibration. of the apparatus, to cause thesensitive relay 58 to operate only when the con.- centration of CO in the atmosphere being analyzed exceeds a predetermined value.

Energization of the sensitive relay 53 operates to complete a circuit to a more rugged relay 338 by connecting it across the line conductors Ll, L2. Energization of the relay 333, completes acircuit between L2 and output conductor 343, the other output conductor 34! being connected to LI. The indicator lamp 64, in series with a voltage: dropping resistor 342, is connected across the output conductors 349, 34 I.

Operation In using the apparatus, the intake tube- 20- is connected to the space.- from which the air is to be drawn for the purpose of analysis, and the main switch 330 is closed. As previously men-- tioned, the closure of th s switch will result in starting of. the pump motor 88, energization of the cell heating element 308 (if. the cell is at a: temperature lower than 120 FL), and energize;- tion of the timing motor 3332.

Assuming. that the. main switch is closed at the beginning of a. cycle, the switch 334 will be closed and the switch 335 open, and these switches will remain. in their respective conditions for a pre determined period,. such as 30 seconds. The pump or air compressor 24 will supply air under pressure to cause its circulation through the various paths previously described with reference to Fig. 2. Since the pump operates at high speed, in the order of 6000 R. P. M., and since it has a substantial displacement (e. g., 0.25 bore and 0.25" stroke), the air in the system will rapidly be raised to a pressure at which the pressure relief valve 42 opens to permit escape of air from the system. 7

' Assuming that the saturator contains an ample supply of distilled water, and that the cell 38 is amply supplied with the K01 solution, as may be readily determined from observation of the liquid level gauges 62 and Gil, the apparatus commences operating.

It will be understood that during normal operation the spring 244 holds the two-way valve in the position in which it is shown in Fig. 10, so that the air leaving the soda lime filter 32 will divide at the T 210 and will flow at substantially equal rates through the two flow meters 34 and 48. The rates of flow may, of course, be readily adjusted by means of the needle valves 224, observing the indications in the flow meters to secure this regulation. Since both the pressure relief valves 26 and 42 operate to permit escape of air from the system at predetermined absolute pressures, the air between these two valves will, during operation. be maintained. at a constant pressure irrespective of the pressure from which the air is drawn or the atmosphere into which it is discharged. Thus the apparatus may be used with equal effectiveness and accuracy at sea level or any other elevation at which the airplane may be flying. Having initially adjusted the needle valves 224 to secure equal flow rates through the two parallel flow paths, they will not require frequent readjustment.

The air being substantially. completely saturated with water vapor in passing through the saturator 30, it will have CO2, S02, and similar gases removed as it passes through the soda lime filter 32. However, this filter will not remove CO from the gas mixture. During the assumed first half of the cycle of operation, the burner is energized and hence any CO in that portion of the sample which passes through the burner 46 will combine with the oxygen of the air to form CO2, due to the heating and possibly catalytic effect of the incandescent platinum in the burner. It will be readily apparent that the concentration of CO2 will be proportional to the concentration of CO in the air being analyzed.

The sample of air containing the CO2 enters the chimney 208 and the CO2 is dissolved in the K01 solution therein, thereby increasing its hydrogen ion concentration, as stated above. The other portion of the sample which is supplied to the chimney 269, contains the CO which is not appreciably soluble in the KCl solution, and which does not appreciably change its hydrogen ion concentration. The solutions in the two chimneys come into mutual contact by virtue of the perforations 288 therein so that a diiference in potential will appear across the platinum electrodes 286 and 281 as a result of the mutual contact of said solutions at diiferent hydrogen ion concentrations.

Upon completion of the first half of the cycle, the timing motor 332 will operate to close switch 335 and open'switch 334, thus completin the circuit between the electrodes of the cell and the winding of the sensitive relay 58, and deenergizing the burner 46. Assuming that there was a small percentage of CO in the air sample being analyzed, there will have been sufiicient potential difference between the two electrode 236 and 237 to cause operation of the sensitive relay 58 and the latter will therefore in turn operate the relay 338. The circuit completed by the relay 333 will be through the indicator lamp 54 withits series resistor 342 and through any other conthe same and the cell thus put in normal condition.

As the air leaves the chimneys 258, 269, the water spray is separated therefrom by the perforated caps 216, 211'! as well as by the separator or rectifier 49, so that the supply of the solution in the cell 38 will not be depleted.

Theory of operation The pump 24 has suflicient capacity that even at high altitudes it will maintain the required pressure within the system. Under most condi tions of operation, surplus air supplied by the pump will continuously escape from the pressure relief valve 25. The check valve 28 is pro-' vided merely as a safety measure to prevent reverse fiow of liquid from the saturator 30 in the event that the pump 24 should be stopped either accidentally or when the system is shut off.

In order to calibrate the apparatus, it is desirable to connect the inlet 20 to a source of air containing a known percentage of CO2. In most 10- cations, the CO2 in the atmosphere will have a concentration sufficiently invariable that the atmosphere may be used as a calibrating sample. When making the calibration, the valve 44 is manually operated to connect the pipe I98 to the pipe 248 which leads to the burner 46. The other part of the sample passes through the soda lime filter 32 where the CO2 is removed. Thus the chimney tube 268 is supplied with air containing CO2, while the air supplied to the chimney tube 239 does not contain CO2. For these test purposes, a meter may be connected across the cell 38 and the meter thus calibrated. In addition, the variable resistor 336 may be adjusted so as to cause operation of the sensitive relay 53 when the concentration of CO reaches a predetermined value.

The apparatus shown is extremely sensitive and may be adjusted to cause the operation of the sensitive relay 58 when the concentration of CO in the atmosphere being analyzed is in the order of ten parts in a million.

The apparatus and its method of operation are such that its sensitivity increases with decreasing concentration of CO. This may be explained by the fact that the potential developed across the electrodes 286, 28'! is determined by the logarithm of the ratio of the activity of the solution in one of the chimneys 268 relative to the activity of the solution in the other chimney 269.

The electrochemical formula may, for the sake of simplicity, be reduced to the following equaacross the electrodes; K is a constant; a is the activity of the solution in the chimney 268, and

a -1e the activity of the solution in the chimney $9. Since the temperature and ressure within the two chimneys are equal, thesef'actors, as well asothers, need not be considered, or may be assumed to be included within the constant From this formula it will be apparent that as (1" decreases in value by a factor of 1 for example from 0.010 (logarithm-2.00)" to 0.001 (logarithm-3106 the electrical potential differences across the electrodes will change by the factor 2/3 whereas, when a decreases from 0.001 (10garithmil) to 0.0001 (logarithn1-4')' the potential across the electrodes will change by a factor of 3/4. Because of this relatibnship it appears that under properlycontrolled conditions the apfiaratus of this invention may be employed to de"-- tect concentrations of CO in air" of as low as one ten parts in a billion. This is possible because the potentials developed are not proportional to the" concentrations, but are proportional to the logarithm of the concentration, and" therefore a relatively slight change in concentration causes a greatly magnified (mathematically and actu a-lly)" changein the potential developed.

For ordinary uses, it is not essential that the apparatus give a warning signal on verylow concentrations of CO; For example, when used on aircraft, the apparatus will usually be adjusted. so that the sensitive relay will be operated when the concentration of CO in theair being analyzed is in the" order of 0*.005.

While the principle or o erationof the cell is not thoroughly understood in all its details, it ap' pears that the air electrode phenomenon is'em ploye'd; Apparatus of the type disclosed herein has been operated over long periods of time, ire-'- quently analyzing an atmosphere containing various fumes such as are present in painting and l'acquering and plating departments of a factory; without poisoning the cell and without interfering with the satisfactory operation of the apparatus. It therefore appears that the appara tus maybe used under wide variety of conditions without impairment of function.

The" apparatus disclosed herein was particularl'y designed for use on aircraft where it would subject to Wide variations in temperature and pressure and subject to considerable shock and vibration. Foru'se in analyses of the atmosphere on the" ground, the apparatus could be simplified in many respects. For example, in usin the apparatus in a laboratory it might not be nee essary to provide'the means for heating the cell andpcss'iblythe' rectifier and saturato'r would not be essential. For some purp'oses it might be preferable to have-thepotential across the electrodes indicated or recorded continuously by a meter, in" which eventthe burner would be energized continuously. In some installations it might be desirable to connect a voltage amplifier between the cell and the mot-er. However, under rnost conceivable conditions oi use of the apparatus, the cycling herein described would be; preferable since it makes the use of an amplifier unnecessa'ry, and since the cycling system insures a; more significant potential difference on the electrodes by permitting the potential to accumulate tor a short time.

It; has been found that solutions or materials other'than- KCI may be employed, and: that metals other than platinum be used for the electrodes. However, the use oi platinum electrodes in: a dilute K01. solution hasbeen-foundto cause the cell to generate the highest potentials;

. While I have shown and described a particular embodiment of my invention, it will be apparent to those skilled in the art, that numerous modifications and variations may be made there in without departing from the underlying prin ciples of the invention. I therefore desire, by the following claims, to include within the scope of my invention all such modifications and variations by which substantially the results thereof may be obtained by the use of the same or substantially the same means.

I claim: 1. Apparatus for analyzing air for the presence" of an acid anhydride forming gas comprising, in: combination, a pump having its inlet connected.

' to the source of air to be analyzed, a firstpres sure respon 've relief valve connected by a conduit to the outlet of the pump, a conduit connecting the outlet of said first relief valve, through a check valve and a humidifier, to the inlet of" an absorbent container for removing acid. anhydrides from the air supplied by said pump, bifurcated conduit connected 1 the outlet of said container for dividing the air flowing therefrom into two separate streams of substantially equal flow rates, one fork of said bifurcated conduit being connected with the inlet of a combustion chamber and the other: fork being connected with the inlet of a first flow meter, a burner positioned in; said combustion. chamber for ce sing acid anhydride forming gas in one of the air streams to combine with oxygen therein to form an acid anhydride, a conduit from theoutlet of the combustion chamber to thein'let of a second flow meter, separate conduits from there-- spective outlets of the two fiowmeters to the respective inlets of two absorption chambers mounted, in spaced. apart relationship, in a cell: that. is adapted to be partly filled with a' salt solution, a metallic electrode positioned in each of said absorption chambers; apertures in the walls of said absorption chambers adjacent to said electrodes to provide free communication of said salt solution between said cell and said ab sorption chambers, said electrodes being connected in an" electrical circuit that includes said salt solution, means for indicating the potential diif'erence between" said electrodes and a timer operating cyclically and alternately to energize saidiburn'er and disconnect said indicating means from the electrodes during partof a cycle, and to deenergize said burner and connect said indieating means to said electrodes during the re m'ainder' of the cycle, a reflux closure for each of said absorption chambers located above the level of the salt solution therein, a discharge chamber'in said cell located above the level of the salt solution therein, apertures in said reflux closures to provide forthe flow of air from said absorption chambers into said. discharge chamber, and a conduit connecting said discharge chamber, through an entrainer a second pressure responsive relief valve, to the atmosphere.

2. The combination set forth in claim 1, in which the electrodes are sheets of platinum having a relatively large surface area.

3'. The combination set forth in claim 1, in which the burner comprises a tubular member containing a platinum wire, and a source of else-- trica'l energy connected to the ends of the wire to heat thelatter to incandescence.

4. The combination set forth in claim I, in which the means for indicating the electrical uctential difference of theelectrodes comprises a sensitive relay, and electrical indicating means controlled bythe'relay;

The combination set forth in claim 1, in which said cell is provided with thermostatically controlled heating means operable to maintain it at a predetermined temperature.

6. Apparatus for analyzing air for the presence of an acid anhydride forming gas comprising, in combination, a pump having its inlet connected to the source of air to be analyzed, a first pressure responsive air relief valve connected by a conduit to the outlet of the pump, a conduit connecting the outlet of said first relief valve, through a check valve and a humidifier, to the inlet of an absorbent container for removing acid anhydrides from the air supplied by said pump, a bifurcated conduit connected with the outlet of said container for dividing the air flowing therefrom into two separate streams of substantially equal flow rates, one fork of said bifurcated conduit being connected with the inlet of a com bustion chamber and the other fork being connected with the inlet of a first flow meter, 2. burner positioned in said combustion chamber for causing carbon monoxide in one of the air streams to combine with oxygen therein to form carbon dioxide, a conduit from the outlet of the combustion chamber to the inlet of a second flow meter, separate conduits from the respective outlets of the two flow meters to the respective inlets of two absorption chambers mounted, in spaced apart relationship, in a cell that is adapted to be partly filled with a salt solution, a metallic electrode positioned in each of said absorption chambers, apertures in the walls of said absorption chambers adjacent to said electrodes to provide free communication of said salt solution between said cell and said absorption chambers, said electrodes being connected in an electrical circuit that includes said salt solution, means for indicating the potential differenc between said electrodes and a timer operating cyclically and alternately to energize said burner and disconnect said indicating means from the electrodes during substantially one-half of a cycle, and to deenergize said burner and connect said indicating means to said electrodes during the remainder of the cycle, a reflux closure for each of said absorption chambers located above the level of the salt solution therein, a discharge chamber in said cell located above the level of the salt solution therein, apertures in said reflux closures to pJovide for the flow of air from said absorption chambers into said discharge chamber, and a conduit connecting said discharge chamber, through an entrainer and a second pressure responsive relief valve, to the atmosphere.

' '7. In an apparatus for analyzing air for the presence of carbon monoxide, the combination of compression means for supplying under pressure air to be analyzed, a conduit from the outlet of said compression means to the inl t of an absorber adapted for removing acid anhydrides from the air to be analyzed, a divided conduit for dividing the air flowing from said absorber into two separate streams, one division of said conduit connecting said absorber to the inlet of a combustion chamber with an igniter located therein for causing carbon monoxide in the air stream entering the combustion chamber to combine with oxygen therein to form carbon dioxide, a cell adapted to be partly filled with salt solution, two absorption chambers mounted in said cell, the second division of said divided conduit connecting said absorber to the inlet of one of said absorption chambers, a conduit connecting the outlet of the combustion chamber to the iii inlet of the second absorption chamber, anair disperser in each of said absorption chambers near th inlet thereof, an electrode mounted in. each of said absorption chambers, apertures in the walls of said absorption chambers adjacent to said electrodes to provide free communication: of said salt solution between said cell and said absorption chambers, and an electrical circuitincluding said electrodes, said salt solution and electrical potential indicating means.

8. The combination set forth in claim '7 in which said cell is provided with thermostatically controlled heating means operable to maintain it at a predetermined temperature.

9. In an apparatus for analyzing air for the presence of an acid anhydride forming gas, the combination of compression means for supplying under pressure the air to be analyzed, a conduit from the outlet of said compression means to the inlet of an absorber adapted for removing acid anhydrides from the air to be analyzed, a bifurcated conduit connected with the outlet of said absorber for dividing the air flowing therefrom into two separate streams of substantially equal flow rates, -a first fork of said bifurcated conduit connecting said absorber to the inlet of a combustion chamber with an igniter located therein for causing acid anhydride forming gas in one of said streams of air to combine with oxygen therein to form its acid anhydride, a cell. adapted to contain an aqueous medium, two communicating absorption chambers mounted in said cell, the second fork of said bifurcated conduit connecting said absorber to the inlet of one of said absorption chambers, a conduit connecting the combustion chamber to the inletof the second abzorption chamber, an electrode mounted in each of said absorption chambers, apertures in the walls of said absorption chambers adjacent to said electrodes to provide free communication of said aqueous medium between said cell and said absorption chambers, and an electrical circuit including said electrodes, said aqueous medium and electrical potential indicating means.

10. In an apparatus for analyzing air for the presence of an acid anhydride forming gas, the combination of compression means for supplying under pressure the air to b analyzed, a conduit from the outlet of said compression means to the inlet of an absorber adapted for removing acid anhydrides from the air to be analyzed, a bifurcated conduit connected with the outlet of said absorber for dividing the air flowing therefrom into two separate streams of substantially-equal flow rates, a first fork of said bifurcated conduit connecting said absorber to the inlet of a com. bustion chamber with an igniter located therein for causing acid anhydride forming gas in one of said streams of air to combine with oxygen therein to form its acid anhydride, a cell adapted to contain an aqueous medium, two communicating absorption chambers mounted in said cell, the second fork of said bifurcated conduit connecting said absorber to the inlet of one of said absorption chambers, a conduit connecting the combustion chamber to the inlet of the second absorption chamber, an electrode mounted in each of said absorption chambers, apertures in the walls of said absorption chambers adjacent to said electrodes to provide free communication of said aqueous medium between said cell and said absorption chambers, and an electrical circuit including said electrodes, said aqueous me= dium and electrical potential indicating means. and thermostatically controlled heating means Outside and adjacent to said cell, operable to maintain it at a predetermined temperature.

11. In an apparatus for detection of the presence of carbon monoxide in the atmosphere, the combination of an absorber for removing acid anhydride gases from the air being analyzed, a bifurcated conduit connected with the outlet of said absorber for dividing the air flowing therefrom into two separate streams of substantially equal flow rates, a first fork of said bifurcated conduit connecting said absorber to the inlet of a combustion chamber, a burner located in said combustion chamber for causing any carbon monoxide, contained in the one of said streams of air that enters said combustion chamber, to form carbon dioxide, a cell having a main body adapted to contain an aqueous solution, two absorption chambers mounted in said cell, the second fork of said bifurcated conduit connecting with the inlet of one of said absorption chambers, a conduit connecting the combustion chamber to the inlet of the second absorption chamber, an air disperser in each of said absorption chambers near the inlet thereof, an electrode mounted in each of said absorption chambers, and apertures in the walls thereof adjacent to said electrodes to provide for the relatively free flow of the solution from the main body of the cell into and out of the absorption chambers, said electrodes being connected in an electrical circuit that includes said aqueous solution, potential indicating means and a timer operating cyclically and alternately to energize said burner and disconnect said indicating means from the electrodes during part of a cycle, and to deenergize said burner and connect said indicating means to said electrodes during the remainder of the cycle.

12. In an apparatus for detection of the presence of carbon monoxide in the atmosphere, the combination of an absorber for removing acid anhydride gases from the air being analyzed, a bifurcated conduit connected with the outlet of said absorber for dividin the air flowing therefrom into two separate streams of substantially equal fiow rates, a first fork of said bifurcated conduit connecting said absorber to the inlet of a combustion chamber, a burner located in said combustion chamber for causing any carbon monoxide, contained in the one of said streams of air that enters said combustion chamber, to form carbon dioxide, a cell having a main body adapted to contain an aqueous solution, two absorption chambers mounted in said cell, the second fork of said bifurcated conduit connecting with the inlet of one of said absorption chambers, a conduit connecting the combustion chamber to the inlet of the second absorption chamber, an air disperser in each of said absorption chambers near the inlet thereof, an electrode mounted in each of said absorption chambers, and apertures in the walls thereof adjacent to said electrodes to provide for the relatively free flow of the solution from the main body of the cell into and out of the absorption chambers, said electrodes being connected in an electrical circuit that includes said aqueous solution, potential indicating means and a timer operating cyclically and alternately to energize said burner and disconnect said indicating means from the electrodes during substantially one-half of a cycle, and to deenergize said burner and connect said indicating means to said electrodes during the remainder of the cycle.

13. A cell for the determination of the presence of a gaseous anhydride in air by electrically 18 detecting a change in the ionic concentration of an aqueous solution when the anhydride is dissolved therein, comprising a container adapted to be partly filled with a dilute aqueous solution, a pair of tubular elements extending vertically from the bottom of the container, a disperser located at the bottom of each of said tubular elements for admitting thereinto a stream of air, an electrode comprising a metallic sheet of substantial surface area mounted in each of said tubular elements, and apertures located in the walls of said tubular elements adjacent to said electrodes to provide free communication for said solution between said container, said tubular elements and said electrodes.

14. In an apparatus for the detection of the presence of carbon monoxide in the atmosphere, the combination of an absorber for removing acid anhydride gases from the air being analyzed, a ibifurcated conduit connected with the outlet of said absorber for dividing the air flowing therefrom into two streams having substantially equal flow rates, one fork of said bifurcated conduit connecting with the inlet of a combustion chamber, a burner located in said combustion chamber for burning any carbon monoxide in the one of said streams flowing into said combustion chamber to form carbon dioxide, a cell having a main body adapted to contain an aqueous solution, two absorption chambers mounted in said cell, the second fork of said bifurcated conduit connecting said absorber to the inlet of one of said absorption chambers, a conduit conmeeting the outlet of the combustion chamber to the inlet of the second absorption chamber, an electrode mounted in each of said absorption chambers, apertures in the walls of said absorption chambers adjacent to said electrodes to provide free communication of said aqueous solution between said cell and said absorption chambers, and an electrical circuit including said electrodes, said aqueous solution and electrical potential indicating means.

WILLIAM F. FAGEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 870,675 Guess et al. Nov. 12, 1907 1,008,485 Metzger Nov. 14, 1911 1,236,000 Neeley Aug. 7, 1917 1,375,933 Rideal et al Apr. 26, 1921 1,475,000 Cooper et al. Nov. 20, 1923 1,670,819 Morris et al. May 22, 1928 1,877,296 Goldberg Sept. 13, 1932 1,883,328 Bihl et al Oct. 18, 1932 1,893,490 Beekley Jan. 10, 1933 1,931,135 McLaughlin et al. Oct. 17, 1933 2,079,601 Canfield May 11, 1937 2,149,441 Jacobson Mar. 7, 1939 2,160,326 Carbonara May 30, 1939 2,168,236 Pick Aug. 1, 1939 2,190,302 Waldschmidt Feb. 13, 1940 2,288,180 Brengman et al. June 30, 1942 2,354,915 Granberg Aug. 1, 1944 FOREIGN PATENTS Number Country Date 300,281 Great Britain Sept. 12, 1929 416,900 Great Britain Sept. 24, 1934 499,795 France Nov. 28, 1919 

9. IN AN APPARATUS FOR ANALYZING AIR FOR THE PRESENCE OF AN ACID ANHYDRIDE FORMING GAS, THE COMBINATION OF COMPRESSION MEANS FOR SUPPLYING UNDER PRESSURE THE AIR TO BE ANALYZED, A CONDUIT FROM THE OUTLET OF SAID COMPRESSION MEANS TO THE INLET OF AN ABSORBER ADAPTED FOR REMOVING ACID ANHYDRIDES FROM THE AIR TO BE ANALYZED, A BIFURCATED CONDUIT CONNECTED WITH THE OUTLET OF SAID ABSORBER FOR DIVIDING THE AIR FLOWING THEREFROM INTO TWO SEPARATE STREAMS OF SUBSTANTIALLY EQUAL FLOW RATES, A FIRST FORK OF SAID BIFURCATED CONDUIT CONNECTING SAID ABSORBER TO THE INLET OF A COMBUSTION CHAMBER WITH AN IGNITER LOCATED THEREIN FOR CAUSING ACID ANHYDRIDE FORMING GAS IN ONE OF SAID STREAMS OF AIR TO COMBINE WITH OXYGEN THEREIN TO FORM ITS ACID ANHYDRIDE, A CELL ADAPTED TO CONTAIN AN AQUEOUS MEDIUM, TWO COMMUNICATING ABSORPTION CHAMBERS MOUNTED IN SAID CELL, THE SECOND FORK OF SAID BIFURCATED CONDUIT CONNECTING SAID ABSORBER TO THE INLET OF ONE OF SAID ABSORPTION CHAMBERS, A CONDUIT CONNECTING THE COMBUSTION CHAMBER TO THE INLET OF THE SECOND ABSORPTION CHAMBER, AN ELECTRODE MOUNTED IN EACH OF SAID ABSORPTION CHAMBERS, APERTURES IN THE WALLS OF SAID ABSORPTION CHAMBERS ADJACENT TO SAID ELECTRODES TO PROVIDE FREE COMMUNICATION OF SAID AQUEOUS MEDIUM BETWEEN SAID CELL AND SAID ABSORPTION CHAMBERS, AND AN ELECTRICAL CIRCUIT INCLUDING SAID ELECTRODES, SAID AQUEOUS MEDIUM AND ELECTRICAL POTENTIAL INDICATING MEANS.
 13. A CELL FOR THE DETERMINATION OF THE PRESENCE OF A GASEOUS ANHYDRIDE IN AIR BY ELECTRICALLY DETECTING A CHANGE IN THE IONIC CONCENTRATION OF AN AQUEOUS SOLUTION WHEN THE ANHYDRIDE IS DISSOLVED THEREIN, COMPRISING A CONTAINER ADAPTED TO BE PARTLY FILLED WITH A DILUTE AQUEOUS SOLUTION, A PAIR OF TUBULAR ELEMENTS EXTENDING VERTICALLY FROM THE BOTTOM OF THE CONTAINER, A DISPERSER LOCATED AT THE BOTTOM OF EACH OF SAID TUBULAR ELEMENTS FOR ADMITTING THEREINTO A STREAM OF AIR, AN ELECTRODE COMPRISING A METALLIC SHEET OF SUBSTANTIAL SURFACE AREA MOUNTED IN EACH OF SAID TUBULAR ELEMENTS, AND APERTURES LOCATED IN THE WALLS OF SAID TUBULAR ELEMENTS ADJACENT TO SAID ELECTRODES TO PROVIDE FREE COMMUNICATION FOR SAID SOLUTION BETWEEN SAID CONTAINER, SAID TUBULAR ELEMENTS AND SAID ELECTRODES. 